Create a hosted map style. Provide a name and optionally a theme document ({base: "light"|"dark", palette: {slot: colour}, layers: {layer_id: overrides}}); omitted, the style starts from the default theme. A theme may also set worldview (ISO 3166-1 alpha-2, accepted: AE, KR, SA, US) to display that jurisdiction's official names for a small curated registry of renamed features; omitted, labels keep the OSM on-the-ground names. Returns the generated style_id (pass it to set_palette / set_layer_paint) and the compiled style URL for MapLibre.